Method for the termination of polymers obtained by the anionic polymerization of dienic and/or vinylaromatic monomers, and compounds suitable to that purpose

ABSTRACT

Coupling agents of general formula ##STR1## and their use in a method for the termination of living polymers obtained by the anionic polymerization of dienic and/or vinylaromatic monomers.

The anionic polymerization, if carried out under proper conditions andstarting from suitable monomers (M. SZWARC, Carbanions, Living Polymersand El. Transfer Processes, Interscience Publishers, J. Wiley and Sons,New York, 1968), allows living polymers to be obtained, which are wellfit for suitable transformations. Among these, the reaction of coupling(uniting two or more polymeric segments through a linking agent to yielda polymer having molecular weight nPM, wherein PM is the molecularweight of the polymeric segment and n is the functionality of thelinking agent) is certainly one of the most investigated processes,because it allows, by a simple approach, important changes to beobtained also in terms of properties of the polymers processed.

For example, in case of polymerization of dienes, by this way increasingMooney viscosity, reducing the "cold flow", increasing the "greentensile strength" and even succeeding in modifying the molecular weightas desired is possible.

In case then of the synthesis of block polymers constituted by linear orbranched couplings of A-B elements (wherein A is an aromatic polyvinyland/or polyisopropenyl sequence and B is a dienic sequence, alsohydrogenated), the use of efficient coupling agents becomes a factor ofbasic importance because, as known, the possible presence of unreactedA-B products in the end product impairs the technological properties ofthe same.

In the technical literature, numerous examples are reported of couplingagents [H. L. HSIEH, Rubber Chem. and Tech. 49 (5), 1305 (1976)].

We have found now that the hereunder exemplified compounds can beconveniently used as new coupling agents, because, besides theproperties typical of the best coupling agents described in technicalliterature (cfr. H. L. Hsieh, ibid.), they show the followingadvantages:

(i) the coupling reaction can be accomplished without the use ofactivators;

(ii) the coupling reaction can be accomplished at a temperature lowerthan that normally used for the traditional coupling agents, with thereaction time being the same;

(iii) no side products are formed, because the coupling reaction is anaddition, and not a removal reaction.

The products which we found to be efficient coupling agents arecomprised within the following general formula: ##STR2## wherein:X=aryl, condensed aryl, aryl isolated by a heteroatom or by an alkenylgroup, alkyl with a number of C atoms comprised between 2 and 20,cycloalkyl, alkylcycloalkyl, radical with heteroatom; all these groupspossibly containing a functional group of vinylaromatic, ester,aldehydic, ketonic, cyano type, and so forth;

Y=aryl, cycloalkyl, alkyl, alkylaryl, alkylcycloalkyl, possiblycontaining a functional group of vinylaromatic, ester, aldehydic,ketonic, cyano type, and so forth;

n=an integer, comprised within the range of from 1 to 4;

n'=an integer, comprised within the range of from 1 to 4;

R=H or alkyl group, but preferably H;

Z=Aryl, alkyl, cycloalkyl, possibly containing a functional group ofvinylaromatic, ester, aldehydic, ketonic, cyano type, etc.

Such coupling agents can be prepared in an easy way, and with yields inmany cases can be quantitative, according to the following procedure:##STR3## with the water formed being removed by azeotropic distillationwith a suitable solvent.

Non limitative examples of the aminic compounds used, possiblycontaining a functional group selected among those simplifiedhereinabove (vinylaromatic, ester, cyano, aldehydic, ketonic, and soforth) [see radical X] are: aminostilbene, methyl aminobenzoate,aminobenzonitrile, aminobenzophenone, butylamine, aniline, cyclohexylamine, p.phenylenediamine, 1,5-diaminonaphthalene, 1,6-diaminohexane,2,6-diaminopyridine, 4,4'-diaminodiphenylether, 4,4'diaminodiphenyl,1,4,5,8-tetraaminonaphthalene, 3,3'-diaminobenzidine.

Non limitative examples of compounds of unsaturated aldehydic type [seeradical Y] possibly containing at least one functional group among thosehereinabove indicated are: 4-cyanocinnamaldehyde,4-carboxymethylcinnamaldehyde, cinnamaldehyde, crotonaldehyde, and soforth . . .

In the synthesis of compounds (I), at least one functional group amongthose listed above must be present in radical X, or in radical Y, on inboth of them.

Non limitative examples of aldehydic and/or ketonic compounds [seeradical Z] possibly containing at least one functional group among thesementioned above are: methyl 4-formylbenzoate, methyl 4-acetylbenzoate,4-cyanobenzaldehyde, 4-formylstilbene, benzaldehyde, cyclohexanaldehyde,p-diacetylbenzene, o-, m- and p-phthalaldehyde,tetramethylenedialdehyde.

Non limitative examples of unsaturated aminic compounds possiblycontaining at least one of the above mentioned functional groups are:ethenamine-2-phenyl-4'-carbomethoxy, ethenamine-2-phenyl-4'-cyano,ethenamine-2-phenyl, ethenamine-2-alkyl.

In the synthesis of compounds (II), at least one functional group amongthose reported above must be present in radical Z or in radical Y, or inboth of them.

The compounds of the present patent application can be used in processesfor the polymerization of monomers susceptible of anionic initiationunder livingness conditions, and in particular for the polymerization ofdienic and/or vinylaromatic monomers.

The conjugated dienes used contain from 4 to 12, and preferably from 4to 8 carbon atoms.

Such monomers comprise: 1,3-butadiene, isoprene, 2,3-dimethylbutadiene,piperylene, 3-butyl-1,3-octadiene and 2-phenyl-1,3-butadiene.

The vinylaromatic monomers contain from 8 to 20, and preferably from 8to 14 carbon atoms. Typical examples are: styrene, α-methylstyrene,1-vinylnaphthalene, 2-vinylnaphthalene, 2-isopropenylnaphthalene,p-phenylstyrene, 3-methylstyrene, α-methyl-p-methylstyrene andp-cyclohexylstyrene.

The conjugated dienes and/or the vinylaromatic monomers can bepolymerized either alone or in mixture or sequentially, to formhomopolymers, random copolymers and block copolymers.

The polymerization is carried out in solution at temperatures comprisedwithin the range of from -100° to +200° C. and preferably of from 0° to100° C., and under a pressure which is the presence of the system underthe temperature conditions used; however, higher or lower pressures arenot contraindicated.

Suitable solvents comprise paraffinic, cycloparaffinic and aromatichydrocarbons. Typical examples are cyclohexane, hexane, pentane,heptane, isooctane, benzene, toluene and mixtures thereof.

As known, small amounts of polar compounds can be added to the solventto the purpose of obtaining, in the polymerization of diene, a1,2-configuration, or of increasing the efficiency of the initiator incase of polymerization of vinylaromatic monomers.

The initiators are the typical anionic initiators normally used to thispurpose.

Preferably, the organometallic compounds of formula R-Me are used,wherein R is an aliphatic, cycloaliphatic or aromatic hydrocarbonradical and Me is an alkali metal, preferably lithium.

The amount of initiator used is related to the molecular weight of thepolymer which one wishes to obtain. The polymerization is carried outunder such conditions as to secure the livingness of the polymerobtained (M. SZWARC, Carbanions, Living Polymers and El. TransferProcesses, Interscience Publishers, J. Wiley & Sons, New York, 1968).

The coupling agent can be introduced into the reaction medium by anyway, either by one single addition, or by a portionwise addition and atthe desired time.

Preferably, it is introduced at the end of the polymerization, in thedesired amount.

The molar amount of coupling agent (m_(AC)) to be added is given by theformula:

    m.sub.AC =m.sub.CA /f.sub.AC

wherein m_(CA) =mol of active centres of living polymer and f_(AC)=functionality of the coupling agent (besides the presence of reactivegroups --CH═N--, also other additional functional groups exist).

The amount used of coupling agent conditions the coupling yields:obviously, a stoichometric ratio of polymer active centre to couplingagent active centre (by taking into account the functionality thereof)favours the highest yield.

The temperature at which the "coupling" reaction is carried out dependson the type of agent used, on the type of polymer submitted to thereaction, and on other factors, e.g., on the reaction medium: it canvary generally within the range of from 20° to 150° C., but the reactionis preferably carried out between 40° and 80° C.

The contact times are comprised within the range of from some minutes tosome hours: preferably, times comprised within the range of from 10minutes to 2 hours are used.

Sometimes, also polar activators, which improve the coupling rate, canbe used: in the case of the most active coupling compounds hereinclaimed, the use of these activators is not required.

The solvents are those used in the polymerization.

The coupling reaction is carried out under a pressure which is thepressure of the system at the temperature at which the reaction iscarried out, but higher or lower pressures are not contraindicated.

EXAMPLE 1

The polymerization and coupling are carried out inside a reactor of 1liter of capacity, equipped with stirrer, pressure gauge, thermocouplesheath and inlet way for the reactants and the inert gas.

In the order, 500 cm³ of anhydrous cyclohexane, 12 g of styrene and 1,5mmol of Li-sec.butyl are charged, leaving to polymerize at 60° C. forabout 1 hour. At the end, 30 g of butadiene is introduced and thereaction is complete at 60° C. within 1 hour. A very small aliquot ofthis polymer is isolated and submitted to the various analyses. At 60°C., 0.375 mmol is then injected of a solution in cyclohexane ofmethyl-N-[cinnamylidene]p-aminobenzoate. ##STR4##

15 minutes later the polymer, after the addition of 1 g of antioxidizer,is coagulated with an excess of methanol, 42 g being obtained of aproduct which is dried at 60° C. for 15 hours under vacuum.

The properties of the polymers before and after the coupling reactionare reported in Table 1.

                  TABLE 1                                                         ______________________________________                                        Composition.sup.a                                                                           Molecular Weight.sup.b                                                                             Coupling                                   % by weight   g/mol         Gel    Efficiency.sup.c                           Sample                                                                              STY     BUT     ---M.sub.p  %    %                                      ______________________________________                                        A-B   28.5    71.5     35000      0    --                                     A-B-A 28.5    71.5    135000      0    >>95                                   ______________________________________                                         NOTES:                                                                        .sup.a via N.M.R.;                                                            .sup.b ---M.sub.p = peak molecular weight;                                    .sup.c as the ratio of the area, via G.P.C., of the peak of polymer after     the coupling reaction (AB-A), to the area of the peak of polymer before       coupling (AB).                                                           

The polymer A-B-A of Example 1 has the following technologicalproperties:

Elongation: 910%

Ultimate Tensile Strength: 30.6 MPa

whilst the corresponding polymer A-B, with the elongation being thesame, shows an ultimate tensile strength of about 3 MPa.

If, instead of methyl-N-[cinnamylidene]p-aminobenzoate, the couplingagent dichlorodiphenylsilane is used, under the same experimentalconditions, the coupling efficiency is lower than 10%.

EXAMPLE 2

The test 1 is repeated, with the only variant thatp-benzoyl-aniline-N[cinnamylidene] (0.45 mmol) is used, and polymers(A-B and A-B-A) having the properties shown in Table 2 are isolated.

                  TABLE 2                                                         ______________________________________                                        Composition.sup.a                                                                           Molecular Weight.sup.b                                                                             Coupling                                   % by weight   g/mol         Gel    Efficiency.sup.c                           Sample                                                                              STY     BUT     ---M.sub.p  %    %                                      ______________________________________                                        A-B   29      71       37000      0    --                                     A-B-A 29      71      107000      0    ≃95                      ______________________________________                                         NOTES:                                                                        see Table 1.                                                             

EXAMPLE 3

Into the reactor described at Example 1, 50 g of α-methylstyrene and 1.5mmol of Li-sec.butyl are charged, the polymerization being carried outat 20° C. for 1 hour and 15 minutes. At the end, 5 g of butadiene isadded, it being let interact for 15 minutes, and subsequently 500 cm³ ofcyclohexane with 25 g of butadiene is added, making polymerize at 60° C.for 1 hour. A small sample is drawn, and 0.375 mmol ofmethyl-N-[cinnamylidene]p-aminobenzoate is then injected, the couplingreaction being carried out at the temperature of 60° C. for 15 minutes.In the usual way a polymer (43 g) is isolated, which has the propertiesdescribed in Table 3, wherein also the properties of product A-B arereported.

                  TABLE 3                                                         ______________________________________                                        Composition.sup.a                                                             % by weight   Molecular Weight.sup.b                                                                             Coupling                                         α-        g/mol       Gel  Efficiency.sup.c                       Sample                                                                              MeSTY    BUT    ---M.sub.p  %    %                                      ______________________________________                                        A-B   30       70      36000      0    --                                     A-B-A 30       70     136000      0    ≃90                      ______________________________________                                         NOTES:                                                                        see Table 1.                                                             

EXAMPLE 4

The test 1 is repeated, with the only difference that as the couplingagent, 4-carbomethoxy-cynnamaldehyde-anilido ##STR5## is used.

                  TABLE 4                                                         ______________________________________                                        Composition.sup.a                                                                           Molecular Weight.sup.b                                                                             Coupling                                   % by weight   g/mol         Gel    Efficiency.sup.c                           Sample                                                                              STY     BUT     ---M.sub.p  %    %                                      ______________________________________                                        A-B   28.7    71.3     39000      0    --                                     A-B-A 28.7    71.3    151000      0    ≃95                      ______________________________________                                         NOTES:                                                                        see Table 1.                                                             

EXAMPLE 5

The polymerization test is carried out as described at Example 1, but asthe coupling agent,1,6-diaminohexane-N,N'-bis[cinnamylidene-(4'-carbomethoxy)] (0.25 mmol)##STR6## is used.

The data relevant to the polymers isolated is shown in the followingTable.

                  TABLE 5                                                         ______________________________________                                        Composition.sup.a                                                                           Molecular Weight.sup.b                                                                             Coupling                                   % by weight   g/mol         Gel    Efficiency.sup.c                           Sample                                                                              STY     BUT     ---M.sub.p  %    %                                      ______________________________________                                        A-B   29      71       36000      0    --                                     A-B-A 29      71      210000      0    >95                                    ______________________________________                                         NOTES:                                                                        see Table 1.                                                             

EXAMPLE 6

The test is carried out as in Example 1, but instead of butadiene,isoprene is polymerized. As the coupling agent,ethenamine-2-phenyl-N-[benzylidene-4'-(carbomethoxy)] ##STR7## is used.

The data relevant to the polymer isolated (≈42 g) and to thecorresponding product A-B is shown hereunder.

                  TABLE 6                                                         ______________________________________                                        Composition.sup.a                                                                           Molecular Weight.sup.b                                                                             Coupling                                   % by weight   g/mol         Gel    Efficiency.sup.c                           Sample                                                                              STY     BUT     ---M.sub.p  %    %                                      ______________________________________                                        A-B   28.5    71.5     34000      0    --                                     A-B-A 28.5    71.5    124000      0    ≃90                      ______________________________________                                         NOTES:                                                                        see Table 1.                                                             

EXAMPLE 7

In the same equipment as of the above tests, 40 g of butadiene ispolymerized at 60° C. for 1 hour, with 1.5 mmol of Li-sec.butyl in 400cm³ of cyclohexane. At the end, a mixture ofmethyl-N-[cinnamylidene]p-aminobenzoate (0.2 mmol) and1,6-diaminohexane-N,N'-bis[cinnamylidene-(4'-carbomethoxy)] (0.1 mmol)is added, the mixture being let react 15 minutes at 60° C. The G.P.C.chart of the polymer isolated shows the presence of peaks of productshaving different coupling degrees, and with a distribution of molecularweight broader than of polymer A-B.

We claim:
 1. A process for the termination of living macroanionsobtained by the anionic polymerization or copolymerization of dienemonomers or vinylaromatic monomers or mixtures thereof comprisingintroducing into the polymerization mixture either batchwise orincrementally, a coupling agent selected from the group consisting ofmethyl-N[cinnamylidene]-p.amminobenzoate;p.benzoylaniline-N-[cinnamylidene];4-carbomethoxy-cinnamaldehyde-anilido;1,6-diaminohexane,N,N'-bis-[cinnamylidene-(4'carbomethoxy]; andethenamine-2-phenyl-N-[benzylidene-4' (carbomethoxy)].
 2. The process ofclaim 1 further comprising conducting the termination reaction in thepresence of a polar compound capable of enhancing the coupling rate ofsaid coupling agent.
 3. The process of claim 1 wherein the terminationreaction is conducted at a temperature of from 20° to 150° C.
 4. Theprocess of claim 3 wherein the termination reaction is conducted at atemperature of from 40° to 80° C.
 5. The process of claim 1 wherein theamount of the coupling agent (^(m) AC) added to the polymerizationmixture corresponds to the formula:

    m.sub.AC =m.sub.CA /f.sub.AC

wherein m_(CA) is the number of moles of the active centers of thepolymer and f_(AC) is the functionality of the coupling agent.
 6. Theprocess of claim 1 wherein the termination reaction is conducted in thepresence of a solvent selected from paraffinic compounds,cycloparaffinic compounds and aromatic hydrocarbons.